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Polymers Question Paper 7

Level IGCSE

ExamBoard CIE Topic Organic Chemistry Sub-TopicPaper (Extended) Theory Booklet Question Paper 7

83 minutes

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Subject Chemistry

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1 The hydrolysis of complex carbohydrates to simple sugars is catalysed by enzymes called carbohydrases and also by dilute acids.

(a) (i) They are both catalysts. How do enzymes differ from catalysts such as diluteacids?

.............................................................................................................................. [1]

(ii) Explain why ethanol, C2H6O, is not a carbohydrate but glucose, C6H12O6, is acarbohydrate.

....................................................................................................................................

.............................................................................................................................. [2]

(b) Draw the structure of a complex carbohydrate, such as starch. The formula of a simplesugar can be represented by .HO OH


(c) Iodine reacts with starch to form a deep blue colour.

(i) In the experiment illustrated below, samples are removed at intervals and testedwith iodine in potassium iodide solution.

pipette toremove samples

hot water

aqueous starch anda few drops of saliva(saliva contains enzymes)

T ypical results of this experiment are shown in the table.

time / min colour of sample tested with iodine in potassium iodide solution

0 deep blue

10 pale blue

30 colourless

Explain these results.

....................................................................................................................................

....................................................................................................................................

.............................................................................................................................. [3]

(ii) If the experiment was repeated at a higher temperature, 60 °C, all the samples stayedblue. Suggest an explanation.

.............................................................................................................................. [1]

[Total: 10]


2 Lactic acid can be made from corn starch.

CH3 CH COOH

OH

lactic acid

It polymerises to form the polymer, polylactic acid (PLA ) which is biodegradable.

(a) Suggest two advantages that PLA has compared with a polymer made from petroleum.

[2]

(b) The structure of PLA is given below.

CH3 O

CHO C

CH3

O CH

(i) What type of compound contains the group that is circled?

[1]

(ii) Complete the following sentence.

Lactic acid molecules can form this group because they contain both an

group and an group. [2]

(iii) Is the formation of PLA, an addition or condensation polymerisation? Give areason for your choice.

[2]


(c) When lactic acid is heated, acrylic acid is formed.

H H

C C COOH

H OH

H

lactic acid acrylic acid

C C

H

H

H

COOH

[1]

(i) Complete the word equation for the action of heat on lactic acid.

lactic acid → +

(ii) Describe a test that would distinguish between lactic acid and acrylic acid.

test

result for lactic acid

result for acrylic acid [3]

(iii) Describe a test, other than using an indicator, which would show that bothchemicals contain an acid group.

test

result

[2]

[Total: 13]


3 Three of the factors that can influence the rate of a chemical reaction are:

• physical state of the reactants

• light

• the presence of a catalyst

(a) The first recorded dust explosion was in a flour mill in Italy in 1785. Flour containscarbohydrates. Explosions are very fast exothermic reactions.

(i) Use the collision theory to explain why the reaction between the particles of flourand the oxygen in the air is very fast.

[2]

(ii) Write a word equation for this exothermic reaction.

[1]

The decomposition of silver(I) bromide is the basis of film photography. The equation for this decomposition is:

2AgBr 2Ag + Br2 white black

This reaction is photochemical. A piece of white paper was coated with silver(I) bromide and the following experiment was carried out.

paper coated withsilver(I) bromide

not covered

covered withthin paper

covered withthick card

black

grey

white

initiallysome time later with thecard and paper removed

exposureto light

(b) Explain the results.

[3]


(c) The fermentation of glucose is catalysed by enzymes from yeast. Yeast is added toaqueous glucose, the solution starts to bubble and becomes cloudy as more yeastcells are formed.

C6H12O6(aq) 2C2H5OH(aq) + 2CO2(g)

The reaction is exothermic.

Eventually the fermentation stops when the concentration of ethanol is about 12%.

(i) What is an enzyme?

[1]

(ii) Pasteur said that fermentation was respiration in the absence of air. Suggest adefinition of respiration.

[2]

(iii) On a large scale, the reaction mixture is cooled. Suggest a reason why this isnecessary.

[1]

(iv) Why does the fermentation stop? Suggest two reasons.

[2]

(v) When the fermentation stops, there is a mixture of dilute aqueous ethanol andyeast. Suggest a technique which could be used to remove the cloudiness due tothe yeast.

[1]

Name a technique which will separate the ethanol from the ethanol / water mixture.

[1]

[Total: 14]


4 Alkenes are unsaturated hydrocarbons. They undergo addition reactions.

(a) Two of the methods of making alkenes are cracking and the thermal decomposition ofchloroalkanes.

(i) Complete an equation for the cracking of the alkane, decane.

C10H22 → ............................. + ......................................decane

(ii) Propene can be made by the thermal decomposition of chloropropane.Describe how chloropropane can be made from propane.

reagents propane and ..............................

conditions ................................................... [4]

(b) The following alkenes are isomers.

CH3–CH2–CH=CH2 CH3–C=CH2|CH3

(i) Explain why they are isomers.

...................................................................................................................................

...................................................................................................................................

(ii) Give the name and structural formula of another hydrocarbon that is isomeric withthe above.

name ......................................................

structural formula

[4]


(c) Give the name of the product when but-1-ene reacts with each of the following.

steam .........................................................

hydrogen ....................................................

bromine ...................................................... [3]

(d) Alkenes can polymerise.

(i) Deduce the name and structural formula of the monomer from the structure of thepolymer.

H H� �

————C————C————��

CH3 H �n

name of monomer .......................................................

structural formula

(ii) Draw the structure of the polymer formed from the following monomer.

O�

HC C

� CO � CH3

HH

[4]


(iii) Describe the pollution problems caused by the disposal of polymers in landfill sitesand by burning.

landfill sites ...............................................................................................................

...............................................................................................................................[2]

burning ......................................................................................................................

...............................................................................................................................[1]


5 Some of the factors that can determine the rate of a reaction are concentration, temperatureand light intensity.

(a) A small piece of calcium carbonate was added to an excess of hydrochloric acid. Thetime taken for the carbonate to react completely was measured.

CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)

The experiment was repeated at the same temperature, using pieces of calcium carbonateof the same size but with acid of a different concentration. In all the experiments anexcess of acid was used.

(i) Complete the table (assume the rate is proportional to both the acid concentrationand the number of pieces of calcium carbonate). [3]

(ii) Explain why the reaction rate would increase if the temperature was increased.

...................................................................................................................................

...............................................................................................................................[2]

(iii) Explain why the rate of this reaction increases if the piece of carbonate is crushedto a powder.

...............................................................................................................................[1]

(iv) Fine powders mixed with air can explode violently. Name an industrial processwhere there is a risk of this type of explosion.

...................................................................................................................................

...............................................................................................................................[1]

(b) Sodium chlorate(I) decomposes to form oxygen and sodium chloride. This is an exampleof a photochemical reaction. The rate of reaction depends on the intensity of the light.

2NaClO(aq) → 2NaCl(aq) + O2(g)

(i) Describe how the rate of this reaction could be measured.

...................................................................................................................................

...............................................................................................................................[2]

concentration ofacid / mol dm–3 4 2 2 ……….

number of piecesof carbonate 1 111

time / s ………. 80 ………. 160


(ii) How could you show that this reaction is photochemical?

...................................................................................................................................

...............................................................................................................................[1]

(c) Photosynthesis is another example of a photochemical reaction. Glucose and morecomplex carbohydrates are made from carbon dioxide and water.

(i) Complete the equation.

6CO2 + 6H2O → C6H12O6 + ……….. [2]

(ii) Glucose can be represented as

Draw the structure of a more complex carbohydrate that can be formed fromglucose by condensation polymerisation.

HO OH

[2]


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